Perfluorovinyl ether sulfinic acids and salts thereof have utility as initiators in free radical polymerization reactions.
Methods for the synthesis of fluorochemical sulfinates have been reported in the literature. For example, perfluoroalkane sulfinates can be prepared from the corresponding perfluoroalkanehalides via a dehalogenation and sulfination reaction using a sulfite plus an oxidant, hydroxymethane sulfinate, thiourea dioxide or sodium dithionite in water and such cosolvents as acetonitrile, glycol, diethylene glycol and alcohols.
Fluorocarbon sulfinates can also be prepared by reduction of the corresponding perfluoroalkane sulfonyl halides using sulfites, hydrazine, dithionites, and zinc in solvents such as dioxane, dimethoxyethane, di-n-butyl ether, tetrahydrofuran (THF), and diethylene glycol diethyl ether. These methods are reported in U.S. Pat. No. 3,420,877; U.S. Pat. No. 5,285,002 (Grootaert); U.S. Pat. No. 5,639,837 (Farnham et al.); U.S. Pat. No. 6,462,228 (Dams); Japanese Laid Open Patent Publication No. 2006131588 (Aoki); WO 03/10647 (Moll); C. M. Hu, F. L. Quing and W. Y. Huang, J Org Chem, 1991, 2801-2804; W. Y. Huang, Journal of Fluorine Chemistry, 58, 1992, 1-8; W. Y. Huang, B. N. Huang and W. Wang in Acta Chim. Sinica (Engl. Ed.), 1986, 178-184, and Acta Chim. Sinica (Engl. Ed.), 1986, 68-72; F. H. Wu and B. N. Huang, Journal of Fluorine Chemistry, 67, 1994, 233-234; C. M. Hu, F. L. Quing and W. Y. Huang, Journal of Fluorine Chemistry, 42, 1989, 145-148.
For some functionalized starting materials, these methods present several disadvantages, including slow reaction times, large amounts of by-products which typically must be removed from the sulfinate and required use of a cosolvent that may have a negative impact on processes in which the sulfinate is ultimately employed, e.g., free-radical polymerization reactions.
Polymeric fluorosulfinates have also been synthesized by utilizing methods such as reduction of fluorosulfonyl halide polymer side chains and dehalogenation and sulfination of alkyl halide polymer side chains, as reported in U.S. Pat. No. 4,544,458 (Grot et al.) and Japanese Patent No. 52-24176 (Seko et al.).
Although some functionalized polymeric sulfinates have been synthesized with conventional methods, conventional methods of synthesizing the corresponding monomeric functionalized perfluoroalkyl sulfinates have resulted in poor yields and numerous by-products that require additional separation and purification steps. See, for example, U.S. Pat. No. 5,639,837 (Farnham et al.).
Accordingly, there continues to be a need for an improved process for preparing fluorinated sulfinates, particularly functionalized fluorinated sulfinates, that does not require further processing or purification of the resulting reaction mixture. It is further desirable to improve the yield of the fluorinated sulfinate.